HIV-I Rev protein filaments are the best handle on the protein structure (NMR and x-ray have been unsuccessfiil so far). Each protein has two cysteines, titratable so potentially accessible in the filament. A previous attempts at Au-labeling had failed. Long Rev filaments were successfiilly labeled with Au11 and visualized in the STEM. If this is repeated for the cryoEM, it should improve the reconstruction (currently at 3.2 nm).